1. Field of the Invention
The present invention relates to a cap assembly for a rectangular battery, and more particularly, to a cap assembly for a rectangular battery wherein power can be cut off simultaneously when a safety vent is broken due to an increase in internal pressure of a battery.
2. Description of Related Art
A rectangular battery has been widely used as a secondary battery, and contains an electrode assembly in a rectangular case. FIG. 1 shows an example of the rectangular battery. As shown in FIG. 1, a cylindrical or rectangular electrode assembly (not shown), called a jelly-roll, is installed inside a rectangular case 1 having an open upper surface. The jelly-roll is formed by winding anode and cathode plates (not shown) with a separator (not shown) being interposed therebetween as an insulator. A cap assembly 10 is installed at the upper portion of the case 1.
The cap assembly 10 includes a positive electrode portion 11, a negative electrode portion 12 and an insulating plate 13 for electrically insulating the positive and negative electrode portions 11 and 12 from each other.
When the rectangular battery reacts abnormally, the internal pressure in the case 1 increases due to generation of a gas, so the case 1 may be exploded.
Thus, in order to prevent that kind of explosion and reduce the internal pressure in the case 1, a fracture portion 14 for discharging a gas generated during the reaction is formed at the negative electrode portion 12. That is, when the internal pressure of the battery increases, the edges, which is weak in rigidity, of the fracture portion 14 is destroyed to form a safety vent through which the generated gas is discharged.
In the conventional cap assembly, the internal pressure of the battery can be reduced by destroying the fracture portion 14, but the flow of current is not blocked off. Therefore, a short circuit or an electric leakage can be generated after breakdown of the fracture portion.